The invention relates to a guide device in a centrifugal pump having at least one impeller and a diffuser device arranged following the impeller.
In the article "Development of noise and vibration performance of building services pumps" from the periodical WORLD PUMPS, June 1993, Pages 23-28, the most varied sound and noise sources in the operation of a centrifugal pump are described. One of the possible causes are flow-dynamic sound developments because of flow turbulence, flow interruptions as well as cavitation phenomena. These also include the sound development caused by the interaction between the impeller and the diffuser arranged behind it. When the blade ends of an impeller move past the leading edge or edges of a following diffuser, pressure pulsations occur in the flow medium. These are superimposed on the static pressure inside the pump housing. The magnitude of these pressure pulsations as well as their behavior are essentially determined by the distance between the impeller outlet and the inlet into the diffuser. Small distances cause large pressure pulsations which can be decreased by enlarging the distance, but at the cost of a loss of efficiency and negative repercussions on the course of the characteristic curve. Furthermore, it is recommended to change the number of such hindrances behind an impeller. A profile change of the back face of the impeller blades is also suggested.
Other measures are known from WO 91/13259 and DE-OS 24 22 364, by means of which pulsations of the flow stream of centrifugal pumps having a spiral casing are to be avoided. For this purpose, WO 91/13259 envisions an oblique positioning of the trailing edges of the impeller blades and the use of additional intermediate blades. This oblique orientation of the impeller blade ends, which necessarily occurs in the case of spatially curved impeller blades, exhibits a known more favorable pulsation behavior. For this purpose, an oblique positioning was selected, at which the transitions between the trailing edges of the blades and one impeller cover disk are arranged offset by the distance to an adjacent blade on the opposite impeller cover disk. To a certain extent, the transition points between the blade trailing edge and the cover disk are situated in parallel to the axis of rotation, while the course of the blade trailing edge extends by the offset of a blade spacing diagonally between the transition points. In this case, the opposing hydraulic limits and manufacturing limits are disadvantageous since, for hydraulic reasons, the curvature, the outlet angle of the impeller blades as well as their oblique positioning, can only be varied within a relatively small angular range relative to the axis of rotation because otherwise a desired operating point of the pump cannot be achieved. Such changes may lead to losses in efficiency.
In contrast, in DE-OS 24 22 364, an impeller is used in which the number of blade channels and the blade number is increased by the use of an intermediate wall. As the result of the offset arrangement of the blades by half a blade pitch, a pulsation frequency is obtained which is twice as high in comparison to a diffuser apparatus which interacts with a normal impeller. The principle on which this is based envisions a reduction of the rate of flow per blade channel, whereby the pulsation energy is decreased.
Through the U.S. Pat. No. 2,018,097, a simply operating centrifugal pump is known. A radial wheel rotates in a pot-form housing and pumps into an annular space. In the annular space, radial vanes mounted on the inner wall surface of the housing, which vanes extend in screw-form to the pressure side wheel side space. The vanes are arranged in arcuate form on the same diameter. As a result of the missing covering of these vanes, no pressure increase occurs downstream of the impeller. The vanes arranged in the wheel side space conduct the vortex encumbered flow to an outlet.
With the GB-A 112,292, a measure for influencing the cavitation behavior of spiral housed pumps is disclosed. In comparison with conventional spirals which extend over 360.degree., in this case a spiral extending over only 240.degree. is used. 120.degree. of the circumference of the impeller are covered. In this case the respective first half of the impeller cover viewed in the flow direction exhibits a gradual blocking of the impeller outlet cross section, while the second half effects a complete blockage of the impeller outlet cross section. These blocking measures result in a pulsating pump operation which causes noise.
The U.S. Pat. No. 2,362,514 teaches the use of a gap increase between the impeller outlet and the diffuser inlet in turbochargers. The gap has a wedge-form cross section. In this way secondary flows in the transition between the impeller and the diffuser are influenced in order to avoid vibrations. However, this measure causes losses of efficiency.